A typical recessed lighting fixture often includes three major components: a housing, decorative trim, and a junction box. The housing, which is installed in the ceiling between floor joists, provides means for installation of, and a chamber to house a socket and a lamp.
The trim has a decorative function in that it covers the front of the fixture and any imperfections in the opening of the ceiling. The trim also may serve more practical functions. For example, the trim may serve to protect the lamp, to hold and direct the lamp, to create a desired lighting pattern, and to form an insulating seal between the environment in the room and the space above the ceiling.
A common approach to attaching the trim to the housing uses two extension springs attached to the trim and having hooks on their ends. To install the trim, the springs are extended and the hooks are attached to receptacles inside the housing. Subsequent contraction of the extended springs pulls the trim against the ceiling.
Another approach uses torsion springs attached to the trim. The springs are compressed and their legs are placed in receptacles within the housing. Expansion of the torsion springs exert an upward force on the trim.
A third approach uses friction to keep the trim in the housing. Springs, such as leaf springs, mounted on the trim exert radial force on the lamp housing to keep the trim in place. This approach also may employ sharp barbs on the springs, trim, or housing to further secure the trim.
The junction box provides a location to connect the wires of the lighting fixture to the supply wires that provide power to the lamp. Junction boxes typically are placed adjacent to the housing, and also may be mounted on the side of the housing. Wires pass from the junction box to the lamp socket in the housing.